The present invention relates generally to fuel injector rate shaping, and more particularly to front end rate shaping an injection event of a hydraulically actuated fuel injector utilizing a spill passage and a stepped pumping element.
1. Background Art
It has long been known in the art that injector performance can be increased, and undesirable emissions reduced, by controlling the mass flow rate of fuel injected into a combustion chamber during an injection event. It is also believed that the ability to front end rate shape an injection event can further reduce emissions and noise level while increasing injector performance. While a number of fuel injectors have been developed that have limited rate shaping capabilities, the ability to produce some front end rate shapes has not been possible. Therefore, a fuel injector having a broader range of front end rate shaping capabilities would allow engineers to further reduce undesirable emissions while increasing fuel injector performance.
The present invention is directed to overcoming one or more of the problems set forth above and to increasing the ability of hydraulically actuated fuel injector to produce different front end rate shapes.
2. Disclosure of the Invention
A hydraulically actuated fuel injection system according to the present invention comprises at least one hydraulically actuated fuel injector that includes an injector body that defines a fuel pressurization chamber. A pumping element having a stepped top is movably mounted in a pumping bore defined by the injector body, wherein the pumping element defines at least one internal passageway. The pumping element is movable a distance between a first position and a second position. A spill passage defined by the injector body is open to the fuel pressurization chamber via the at least one internal passageway over a portion of the distance.